This invention relates to bandgap reference circuitry, having a wide supply range, that may generate an accurate and stable voltage reference.
Many precision analog circuits operate with supply voltages that are in the 3V and 5V ranges. This is due in part to the increasing use of battery powered systems and semiconductor voltage specifications. In order to reduce the costs of these systems, the analog circuits need to be designed using standard manufacturing processes and devices.
Accurate and stable voltage reference circuits are required in almost every analog chip. Voltage reference circuits are capable of providing substantially constant reference voltages that are designed to be substantially independent of temperature and process variations.
As is known in the art, a bandgap voltage reference is a circuit having a positive temperature coefficient and a negative temperature coefficient that are combined to have a nominally zero temperature coefficient. A voltage with a negative temperature coefficient is derived from the base-emitter voltage of a bipolar transistor and a voltage with a positive temperature coefficient is derived from the difference between two bipolar transistors operating with different current densities. Summing the voltage with the negative temperature coefficient and the voltage with the positive temperature coefficient, according to a proper ratio, will result in a voltage having substantially zero temperature dependence.
The voltage levels of typical voltage reference circuits must remain within a stable and well-defined range in order to maintain a stable voltage reference output. However, in certain low-power devices, such as hard-disc-driving chips, accurate voltage references are needed both for the power-good mode (e.g., in the 3V or 5v ranges) and for low-power modes (e.g., an emergency-retract mode, in which the supply voltage may be as low as 1.8V).
In view of the foregoing, it would be desirable to provide a bandgap voltage reference circuit that may provide a stable voltage reference output under a wide range of supply voltages.